Cavity filters served as frequency choosing devices are widely used in communication field, specifically radio frequency communications field. Filters in a base station are used for choosing communication signals and filtering clutters or interference signals beyond the communication signal frequency. Generally, the cavity filter includes a cavity, a resonance rod, a cover plate and a frequency modulation assembly, and the cover plate is located at the top of the cavity, the resonance rod is located in the cavity, and the frequency modulation assembly is extended into the resonance rod from the cover plate.
As shown in FIG. 1, a conventional frequency modulation assembly includes a self-locking screw 10, a locknut 11, an adjusting cover 12 and a gasket 13. The locknut 11 and the adjusting cover 12 are arranged for locking the self-locking screw 10 to a desired position and inserting the self-locking screw 10 into the resonance rod 14. However, the conventional frequency modulation assembly has the following drawbacks. First, the components are complex which may cause accumulated assembly tolerances during the assembly to reduce the frequency modulation effect. Second, the use of the locknut 11 will increase the cost and reduce the assembly efficiency accordingly.
Therefore, there is a need for providing an improved frequency modulation assembly and a cavity filter to overcome the above-mentioned drawbacks.